Diabetes is a disorder characterized by persistent variable hyperglycemia due to either inadequate production of insulin by the body and/or an inadequate response by the body to insulin. Type I diabetes mellitus (T1D; also known as juvenile onset diabetes or insulin dependent diabetes) is an autoimmune disorder that typically develops in susceptible individuals during childhood, and involves progressive destruction of insulin-producing cells in the Islets of Langerhans of the pancreas. Patients with clinical T1D require regular insulin replacement therapy. Currently millions of people suffer from T1D with the overall incidence increasing at about 3-5% per year in most populations. While approximately 50% of the background risk of T1D is believed to be due to environmental factors, the remainder is due to genetic causes with up to 20 different genes influencing susceptibility to the disorder. Of the genetic influence, approximately 50% appears to involve genetic variations within the human leukocyte antigen (HLA) class II alleles HLA-DR and HLA-DQ.
Large-scale destruction of insulin-producing cells will already have taken place by the time clinical symptoms of T1D appear. The sub-clinical phase of the disease is characterized by the presence of auto-antibodies which target the individual's islet cells (ICAs), insulin (IAAs), glutamic acid decarboxylase (or GADAs) and/or tyrosine phosphatase (IA-2As).
Although there is currently no cure for T1D, early detection can reduce the likelihood of long-term complications, thereby both improving the quality of life and reducing costs resulting from repeated hospitalization. For example, it has been shown that children previously identified as being autoantibody-positive had a much lower hospitalization rate at the time of diagnosis (3.3% versus 44%), lower mean glycohemoglobin one month later, and lower mean insulin dose one year later. Predictive testing thus appears to lessen morbidity and medical costs at diagnosis and may lead to better metabolic function in the early period after diagnosis (1). Although no immunoprevention therapy has yet been identified that will delay or prevent disease, it is likely that such therapies will be more effective when implemented early, for example in the pre-clinical period before the autoimmune response is well advanced and the remaining islets are stressed.
Cases with a positive family history for T1D represent only 10-15% of newly diagnosed patients (2-5), therefore effective public health testing must test all children in order to identify pre diabetes. While the presence of islet autoantibodies is a sensitive and specific predictor of future T1D, autoantibodies appear at varying ages in different individuals, so periodic testing throughout childhood is necessary for prompt detection. Testing for autoantibodies is invasive and expensive, and thus a separate initial screening step is essential for overall cost-effectiveness. Since the peak incidence range for T1D is from about 4 to 15 years, predictive strategies must be applied early in life if they are to be informative.
The HLA-DR-DQ genetic locus is by far the most informative for T1D susceptibility and is estimated to account for approximately 50% of the genetic susceptibility to the disease (6). It has been suggested that HLA Class II genotyping might provide sufficient information for an initial screening step (6-8). Such genetic screening may be performed as early as the newborn period, well before disease onset. Initial HLA genetic screening can be used to identify susceptible children, who are then offered periodic autoantibody testing to detect activation of islet autoimmunity. This approach has been successfully demonstrated in large research studies, such as the Diabetes Auto-Immunity Study of the Young (DAISY) in Colorado (7), the Prospective Assessment of Newborns for Diabetes Autoimmunity (PANDA) in Florida (9), the Diabetes Prediction and Prevention (DIPP) study in Finland (10), and the Diabetes Evaluation in Washington (DEW-IT) study (11). The latter study further minimized cost and invasiveness by performing the HLA screening in coordination with a Washington State Dept. of Health Newborn Screening Program. These studies confirmed the ability of HLA screening to identify high-risk subjects for intervention or follow-up studies, but no consensus strategy for population-based T1D public health screening has emerged from them. Developing such a strategy is challenging because HLA haplotypes and genotypes form a continuum between highly susceptible and highly protective.
Kiviniemi et al. (12) describe a system for screening large numbers of individuals for genetic risk for T1D that employs multiple screening steps requiring large numbers of probes to identify different HLA alleles.
Assays employing DNA hybridization probes directed to a specific region of the HLA-DQβ region to detect a person's susceptibility to autoimmune diseases, such as T1D, are described in U.S. Pat. No. 5,665,548, with probes directed to the HLA-DR4 region and their use in diagnosing susceptibility to T1D being disclosed in U.S. Pat. No. 5,039,606. US Published Patent Application no. US2004/0126794 discloses methods for detecting increased or decreased risk for T1D by detecting the presence of specific HLA-C and/or HLA-A alleles. Methods for predicting autoimmune diabetes by detecting specific HLA Class II alleles are also described in U.S. Pat. No. 6,534,272. U.S. Pat. No. 5,567,809 describes specific primers and probes for HLA-DRβ DNA typing. US Published Patent Application no. US 2008/0026378 describes a method for predicting the onset of T1D comprising determining a subject's HLA genotype, assigning the subject's risk of developing T1D on the basis of the determined HLA genotype, measuring the concentration of at least one amino acid in a biological sample taken from the individual and combining the resulting information to predict the likelihood of onset of T1D.
While several methods for determining susceptibility to T1D using HLA DR-DQ have been described, such methods are high resolution and therefore not cost-effective for routine screening of large numbers of individuals. There thus remains a need in the art for materials and methods that may be effectively employed to screen populations for individuals at risk of developing T1D.